Semiconductor devices are manufactured through microfabrication by lithography using a photoresist material, but are required to be made finer by a pattern rule in accordance with the increase in integration degree and the increase in speed of LSI in recent years. In lithography using exposure to light, which is used as a general-purpose technique at present, the resolution is now approaching the intrinsic limitation associated with the wavelength of the light source.
A light source for lithography, for use in forming a resist pattern, has a shorter wavelength from a KrF excimer laser (248 nm) to an ArF excimer laser (193 nm). As the resist pattern is made finer and finer, however, there arise a problem of resolution or a problem of collapse of the resist pattern after development, and therefore there is demanded for making a resist film thinner. If the resist film is merely made thinner in response to such a demand, it is difficult to achieve a resist pattern having a film thickness sufficient for processing a substrate. Accordingly, there is increasingly required a process in which not only the resist pattern but also a resist underlayer film is prepared between a resist and a semiconductor substrate to be processed and the resist underlayer film is allowed to have a function as a mask at the time of processing the substrate.
Currently, as the resist underlayer film for such a process, various ones are known. Examples can include a resist underlayer film for lithography, having a selection ratio of dry etching rate close to the resist, unlike a conventional resist underlayer film having a high etching rate. As a material for forming such a resist underlayer film for lithography, there has been proposed a material for forming an underlayer film for multilayer resist process, containing a resin component having at least a substituent which releases a terminal group to form a sulfonic acid residue when a predetermined energy is applied, and a solvent (see, for example, Japanese Patent Laid-Open No. 2004-177668). In addition, examples can also include a resist underlayer film for lithography, having a smaller selection ratio of dry etching rate than the resist. As a material for forming such a resist underlayer film for lithography, there has been proposed a resist underlayer film material including a polymer having a specified repeating unit (see, for example, Japanese Patent Laid-Open No. 2004-271838). Furthermore, examples can also include a resist underlayer film for lithography, having a smaller selection ratio of dry etching rate than the semiconductor substrate. As a material for forming such a resist underlayer film for lithography, there has been proposed a resist underlayer film material including a polymer formed by co-polymerizing a repeating unit of acenaphthylene, and a substituted or non-substituted repeating unit having a hydroxy group (see, for example, Japanese Patent Laid-Open No. 2005-250434).
On the other hand, as a material for allowing such a resist underlayer film to have a high etching resistance, an amorphous carbon underlayer film is well known, which is formed by CVD using methane gas, ethane gas, acetylene gas, or the like as a raw material. However, there is demanded, in terms of process, a resist underlayer film material that can form a resist underlayer film in a wet process such as a spin coating method or screen printing.
In addition, as a material that is excellent in optical characteristics and etching resistance and that is capable of being dissolved in a solvent and being applied to a wet process, the present inventors have proposed a composition for forming an underlayer film for lithography, which contains a naphthalene formaldehyde polymer including a specified constituent unit, and an organic solvent (see, for example, International Publication No. WO 2009/072465 and International Publication No. WO 2011/034062).
Meanwhile, with respect to a forming method of an intermediate layer for use in forming a resist underlayer film in a three-layer process, for example, known are a forming method of a silicon nitride film (see, for example, Japanese Patent Laid-Open No. 2002-334869), and a CVD forming method of a silicon nitride film (see, for example, International Publication No. WO 2004/066377). In addition, as an intermediate layer material for a three-layer process, known is a material containing a silsesquioxane-based silicon compound (see, for example, Japanese Patent Laid-Open No. 2007-226170 and Japanese Patent Laid-Open No. 2007-226204).